Semiconductor lasers made of AlGaInN or other nitride III-V compound semiconductors are under active researches and developments as semiconductor lasers capable of emitting light from the blue region to the ultraviolet region required for enhancing the density of optical discs.
Japanese Patents No. 2780691 and 2735057 disclose semiconductor lasers using nitride III-V compound semiconductors. A semiconductor laser disclosed by the former patent is made of nitride semiconductors containing In and Ga, and includes an active layer of a quantum well structure having first and second surfaces, an n-type nitride semiconductor layer made of InxGa1−xN (0≦x<1) in contact with the first surface of the active layer, and a p-type nitride semiconductor layer made of AlyGa1−yN (0<y<1) in contact with the second surface of the active layer. A semiconductor laser disclosed by the latter patent is made of nitride semiconductors containing In and Ga, and includes an active layer having first and second surfaces, a p-type contact layer made of p-type GaN adjacent the second surface of the active layer, and a first p-type clad layer made of a p-type nitride semiconductor containing In and Ga between the second surface of the active layer and the p-type contact layer and having a band gap energy larger than that of the active layer such that the first p-type clad layer is in direct contact with the second surface of the active layer.
When the Inventor actually fabricated a semiconductor laser using the technique disclosed by the former Japanese Patent No. 2780691 for the research purposes, the laser exhibited a high initial deterioration rate in its life test and a tendency of gradually increasing in operation current with time. Additionally, remarkably uneven electroluminescent emission of light was observed.
A semiconductor laser experimentally fabricated by using the technique disclosed by the latter Japanese Patent No. 2735057 exhibited a still remarkable increase of the initial deterioration rate.
It is therefore an object of the invention to provide a semiconductor device made of nitride III-V compound semiconductors, having a sufficiently low initial deterioration rate and a long lifetime, and remarkably reduced in change with time of the operation current and in emission unevenness, as well as a method capable of easily manufacturing such a semiconductor light emitting device.
More generally, an object of the invention is to provide a semiconductor device made of nitride III-V compound semiconductors, elongated in lifetime and remarkably reduced in change with time, as well as a method capable of easily manufacturing such a semiconductor device.
A further object of the invention is to provide a semiconductor light emitting device made of nitride III-V compound semiconductors, elongated in lifetime by improvement of the crystalline quality of its optical waveguide layer, additionally exhibiting high symmetry of intensity distribution of light in far-field images especially in case of a semiconductor laser, and capable of reducing the aspect ratio of the radiation angle (beam divergence angle), as well as a method capable of easily manufacturing such a semiconductor light emitting device.
More generally, the further object of the invention is to provide a semiconductor device made of nitride III-V compound semiconductors, elongated in lifetime and having favorable properties, as well as a method capable of easily manufacturing such a semiconductor device.